/*********************************************
 * vim:sw=8:ts=8:si:et
 * To use the above modeline in vim you must have "set modeline" in your .vimrc
 * Author: Guido Socher
 * Copyright: GPL V2
 *
 * IP, Arp and UDP functions.
 *
 * Title: Microchip ENC28J60 Ethernet Interface Driver
 * Chip type           : ATMEGA88 with ENC28J60
 *********************************************/
#include <avr/io.h>
#include "avr_compat.h"
#include "net.h"
#include "enc28j60.h"

static uint8_t macaddr[6];
static uint8_t ipaddr[4];

// The Ip checksum is calculated over the ip header only starting
// with the header length field and a total length of 20 bytes
// unitl ip.dst
// You must set the IP checksum field to zero before you start
// the calculation.
// len for ip is 20.
//
// For UDP/TCP we do not make up the required pseudo header. Instead we
// use the ip.src and ip.dst fields of the real packet:
// The udp checksum calculation starts with the ip.src field
// Ip.src=4bytes,Ip.dst=4 bytes,Udp header=8bytes + data length=16+len
// You must set the upd checksum field to zero before you start
// the calculation.
// len for udp is: 8 + 8 + data length
//
// For more information on how this algorithm works see:
// http://www.netfor2.com/checksum.html
// http://www.msc.uky.edu/ken/cs471/notes/chap3.htm
// The RFC has also a C code example: http://www.faqs.org/rfcs/rfc1071.html
uint16_t checksum(uint8_t *buf, uint16_t len, uint8_t type)
{
	// type 0=ip
	//      1=udp
	//      2=tcp
	uint32_t sum = 0;

	if (type == 1)
	{
		sum += IP_PROTO_UDP_V; // protocol udp
		// the length here is the length of udp (data+header len)
		// =length - IP addr length
		sum += len - 8; // = real udp len
	}
	if (type == 2)
	{
		sum += IP_PROTO_TCP_V;
		// the length here is the length of tcp (data+header len)
		// =length - IP addr length
		sum += len - 8; // = real tcp len
	}
	// build the sum of 16bit words
	while (len > 1)
	{
		sum += 0xFFFF & (*buf << 8 | *(buf + 1));
		buf += 2;
		len -= 2;
	}
	// if there is a byte left then add it (padded with zero)
	if (len)
	{
		sum += (0xFF & *buf) << 8;
	}
	// now calculate the sum over the bytes in the sum
	// until the result is only 16bit long
	while (sum >> 16)
	{
		sum = (sum & 0xFFFF) + (sum >> 16);
	}
	// build 1's complement:
	return ((uint16_t) sum ^ 0xFFFF);
}

// you must call this function once before you use any of the other functions:
void init_ip_arp_udp(uint8_t *mymac, uint8_t *myip)
{
	uint8_t i = 0;
	while (i < 4)
	{
		ipaddr[i] = myip[i];
		i++;
	}
	i = 0;
	while (i < 6)
	{
		macaddr[i] = mymac[i];
		i++;
	}
}

uint8_t eth_type_is_arp_and_my_ip(uint8_t *buf, uint8_t len)
{
	uint8_t i = 0;
	//
	if (len < 41)
	{
		return (0);
	}
	if (buf[ETH_TYPE_H_P] != ETHTYPE_ARP_H_V || buf[ETH_TYPE_L_P]
			!= ETHTYPE_ARP_L_V)
	{
		return (0);
	}
	while (i < 4)
	{
		if (buf[ETH_ARP_DST_IP_P+i] != ipaddr[i])
		{
			return (0);
		}
		i++;
	}
	return (1);
}

uint8_t eth_type_is_ip_and_my_ip(uint8_t *buf, uint8_t len)
{
	uint8_t i = 0;
	//eth+ip+udp header is 42
	if (len < 42)
	{
		return (0);
	}
	if (buf[ETH_TYPE_H_P] != ETHTYPE_IP_H_V || buf[ETH_TYPE_L_P]
			!= ETHTYPE_IP_L_V)
	{
		return (0);
	}
	while (i < 4)
	{
		if (buf[IP_DST_P+i] != ipaddr[i])
		{
			return (0);
		}
		i++;
	}
	return (1);
}
// make a return eth header from a received eth packet
void make_eth(uint8_t *buf)
{
	uint8_t i = 0;
	//
	//copy the destination mac from the source and fill my mac into src
	while (i < 6)
	{
		buf[ETH_DST_MAC +i] = buf[ETH_SRC_MAC +i];
		buf[ETH_SRC_MAC +i] = macaddr[i];
		i++;
	}
}

// make a return ip header from a received ip packet
void make_ip(uint8_t *buf)
{
	uint8_t i = 0;
	uint16_t ck;
	while (i < 4)
	{
		buf[IP_DST_P+i] = buf[IP_SRC_P+i];
		buf[IP_SRC_P+i] = ipaddr[i];
		i++;
	}
	// clear the 2 byte checksum
	buf[IP_CHECKSUM_P] = 0;
	buf[IP_CHECKSUM_P+1] = 0;
	buf[IP_FLAGS_P] = 0x40; // don't fragment
	buf[IP_FLAGS_P+1] = 0; // fragement offset
	buf[IP_TTL_P] = 64; // ttl
	// calculate the checksum:
	ck = checksum(&buf[IP_P], IP_HEADER_LEN,0);
	buf[IP_CHECKSUM_P] = ck >> 8;
	buf[IP_CHECKSUM_P+1] = ck & 0xff;
}

void make_arp_answer_from_request(uint8_t *buf, uint8_t len)
{
	uint8_t i = 0;
	//
	make_eth(buf);
	buf[ETH_ARP_OPCODE_H_P] = ETH_ARP_OPCODE_REPLY_H_V;
	buf[ETH_ARP_OPCODE_L_P] = ETH_ARP_OPCODE_REPLY_L_V;
	// fill the mac addresses:
	while (i < 6)
	{
		buf[ETH_ARP_DST_MAC_P+i] = buf[ETH_ARP_SRC_MAC_P+i];
		buf[ETH_ARP_SRC_MAC_P+i] = macaddr[i];
		i++;
	}
	i = 0;
	while (i < 4)
	{
		buf[ETH_ARP_DST_IP_P+i] = buf[ETH_ARP_SRC_IP_P+i];
		buf[ETH_ARP_SRC_IP_P+i] = ipaddr[i];
		i++;
	}
	// eth+arp is 42 bytes:
	ENC28J60PacketSend(42, buf);
}

void make_echo_reply_from_request(uint8_t *buf, uint8_t len)
{
	make_eth(buf);
	make_ip(buf);
	buf[ICMP_TYPE_P] = ICMP_TYPE_ECHOREPLY_V;
	// we changed only the icmp.type field from request(=8) to reply(=0).
	// we can therefore easily correct the checksum:
	if (buf[ICMP_CHECKSUM_P] > (0xff - 0x08))
	{
		buf[ICMP_CHECKSUM_P+1]++;
	}
	buf[ICMP_CHECKSUM_P] += 0x08;
	//
	ENC28J60PacketSend(len, buf);
}

// you can send a max of 220 bytes of data
void make_udp_reply_from_request(uint8_t *buf, char *data, uint8_t datalen,
		uint16_t port)
{
	uint8_t i = 0;
	uint16_t ck;
	make_eth(buf);
	if (datalen > 220)
	{
		datalen = 220;
	}
	// total length field in the IP header must be set:
	buf[IP_TOTLEN_H_P] = 0;
	buf[IP_TOTLEN_L_P] = IP_HEADER_LEN+UDP_HEADER_LEN + datalen;
	make_ip(buf);
	// send to port:
	//buf[UDP_DST_PORT_H_P]=port>>8;
	//buf[UDP_DST_PORT_L_P]=port & 0xff;
	// sent to port of sender and use "port" as own source:
	buf[UDP_DST_PORT_H_P] = buf[UDP_SRC_PORT_H_P];
	buf[UDP_DST_PORT_L_P] = buf[UDP_SRC_PORT_L_P];
	buf[UDP_SRC_PORT_H_P] = port >> 8;
	buf[UDP_SRC_PORT_L_P] = port & 0xff;
	// source port does not matter and is what the sender used.
	// calculte the udp length:
	buf[UDP_LEN_H_P] = 0;
	buf[UDP_LEN_L_P] = UDP_HEADER_LEN+datalen;
	// zero the checksum
	buf[UDP_CHECKSUM_H_P] = 0;
	buf[UDP_CHECKSUM_L_P] = 0;
	// copy the data:
	while (i < datalen)
	{
		buf[UDP_DATA_P+i] = data[i];
		i++;
	}
	ck = checksum(&buf[IP_SRC_P], 16 + datalen, 1);
	buf[UDP_CHECKSUM_H_P] = ck >> 8;
	buf[UDP_CHECKSUM_L_P] = ck & 0xff;
	ENC28J60PacketSend(UDP_HEADER_LEN+IP_HEADER_LEN + ETH_HEADER_LEN + datalen,
			buf);
}
/* end of ip_arp_udp.c */
